#include <stdio.h>

int main()
{
	int number;
	int sum = 0;
	int count = 0;
	
	do{
	   scanf("%d",&number);
	   if (number != -1){
		  sum += number;
		  count ++;
        }
	}while(number != -1); 
	
	printf("%f",1.0*sum/count);
	
	return 0;
}
